This invention relates generally to methods for protecting metallic objects and the like from injury arising from deleterious environmental characteristics, and more particularly relates to a method for providing a metallic object with a protective coating having lubricious character. This invention also relates to a novel coating for both protecting and providing lubricity to a metallic object intended to be subjected to prolonged exposure in a salt-water environment and the like.
The coating of metallic articles exposed to corrosive elements, such as may be found in petrochemical and undersea environments, is well known, and the prior art is prolix with attempts to provide long lasting corrosion-resistant coatings for metals used in structures and equipment exposed to such environments. It is known, for example, to plate or clad metals with other (more active) metals, thereby permitting the plated or clad metal to corrode in lieu of the base metal. Thus, galvanized iron obtains its corrosion-resistant character by sacrificing its coating of zinc in lieu of the iron therebeneath. Similarly, high-purity aluminum or aluminum-copper alloys, and also cadmium alloyed with tin, steel, nickel, and copper, are used in the same manner to coat the underlying metal or alloy sought to be protected. It is further known to plate metals with unalloyed nickel, cadmium, zinc, and other metals that are normally cathodic with respect to the base metal.
Another group of corrosion-resistant coatings, include such materials as chemical conversion coatings constituting stable films on the metal sought to be protected. An example of such a coating is the film formed on a metal article when it is exposed to a phosphate of the same metal. Additionally, inhibitors such as molybdenum have been used in a sulfate solution to form the film on the metal article. However, such films are susceptible to penetration by concentrations of specific anions which are corrosive to the base metal.
However, the corrosion-resistant coatings of the prior art, while effectively protecting the metal articles, may themselves become corroded to such an extent that two interconnected parts, such as comprise a fastener, may require descaling or torch-cutting to separate the parts. In some environments, the use of a torch to separate the interconnected parts is a highly complicated process. Further, some corrosive environments also contain explosive mixtures, wherein even the simple steps of descaling, such as with a wire brush, may create a spark which will ignite the explosive mixtures.
These and other disadvantages of the prior art are overcome with the present invention, wherein novel methods of providing a metallic article with a lubricious, corrosion-resistant coating are disclosed herein.